hamas says israel is killing civilians. this sixth day of air strike follows an israeli offense on sunday leading to the deadliest day of attacks yesterday. at least 29 palestinians were killed including four children when a bomb hit this apartment building. israeli officials say hamas is using civilian buildings as cover to launch rockets across the border. in tel aviv, people on the street ran for cover when sirens signaled an approaching rocket. israel's iron dome defense system has intercepted more than 240 rockets. during a trip to asia, president obama warned israel about expanding into a ground war but he defended israel's fighting back. >> there's no country on earth that would tolerate missiles raining down on its citizens from outside its borders. >> reporter: u.n. secretary- general ban ki-moon is in cairo, egypt today to assist cease-fire talks there. the threat of a ground war remains. thousands of israeli tanks, soldiers and rocket launchers are ready to cross the border awaiting the command. susan mcginnis, c